Laboratory & Inspection Practice
Proficiency testing and interlaboratory comparisons
How to select PT providers, interpret results, and close the loop on issues.
Why this matters
Credible accreditation depends on consistent methods, clear decisions, and evidence that stands up to independent review. This publication translates essential expectations into practical steps so teams can prepare, communicate, and operate with confidence.
Key requirements and expectations
- Link technical competence to methods, equipment, and personnel.
- Demonstrate control of critical technical activities.
- Show traceability, uncertainty, and data integrity.
- Maintain records that prove repeatability and validity.
- PT participation should cover the full accredited scope.
- Results must be reviewed and trended over time.
- Corrective actions are required when results are unsatisfactory.
Evidence and records to prepare
- Method validation or verification records and approvals.
- Calibration certificates and equipment maintenance logs.
- Training and authorization records for technical staff.
- Proficiency testing results and follow-up actions.
- PT participation records and corrective action logs.
Common pitfalls to avoid
- Using unvalidated methods or undocumented deviations.
- Incomplete measurement uncertainty or traceability chains.
- Missing training records for authorized signatories.
- Sampling or chain-of-custody steps not controlled.
- Treating PT failures as one-off issues without root cause.
Practical checklist
- Confirm methods are validated or verified for intended use.
- Maintain up-to-date equipment and calibration schedules.
- Document staff competence and authorization limits.
- Review PT and QA results before external assessment.
- Maintain a PT plan that maps to each method.